Armoring protection of earthfill dams

Because of the increased public awareness for dam safety, more accurate inflow design flood analysis procedures, updated inventories of state-regulated dams, and greater state attention to deficient spillways over the last fifteen years, many of the nation's existing dams are still considered to have inadequate spillway capacity. Expensive remedial measures of spillway enlargement, increased reservoir capacity and combination of these discourage many dam owners, especially private dam owners, from rehabilitating their dams. A possible alternative to expensive rehabilitation of earthen embankment dams, whose spillways are found inadequate to pass the required inflow design flood, is found in erosion protection of, or armoring, the crest and slopes. For this alternative one or more types of armor are placed on the crest and slopes, and the structure is allowed to overtop. Among the armoring options to be discussed in the paper are vegetation, geotextiles, riprap, gabions, cements (roller-compacted concrete and soil cement), and prefabricated concrete blocks (cellular, and wedge-shaped). This thesis includes a brief description of each method mentioned, a discussion of tests conducted by various agencies, a summary of benefits and limitations of each, and a recent survey of state dam safety officials about the use of armoring. This thesis will summarize the responses from each state to the following survey questions about allowing overtopping and the use of armoring: (1) Does your state have any procedures which allow embankment overtopping?, (2) Does your state allow the option of any kinds of embankment protection or armoring for inadequate spillway capacity?, and (3) If protection is allowable, are there any conditions or limitations to what could be done?.

In addition, this thesis will discuss the hydraulic and economic feasibility of using armor protection for the rehabilitation of the Tennessee Valley Authority's Chickamauga Dam.